diff --git a/diff-sha.sh b/diff-sha.sh
index 7e2c0523..5dcdc39e 100644
--- a/diff-sha.sh
+++ b/diff-sha.sh
@@ -7,11 +7,16 @@ GITHUB_OUTPUT=${GITHUB_OUTPUT:-""}
 EXTRA_ARGS="--no-tags"
 PREVIOUS_SHA=""
 CURRENT_SHA=""
+DIFF="..."
 
 if [[ "$GITHUB_REF" == "refs/tags/"* ]]; then
   EXTRA_ARGS=""
 fi
 
+if [[ "$GITHUB_EVENT_HEAD_REPO_FORK" == "true" ]]; then
+  DIFF=".."
+fi
+
 echo "::group::changed-files-diff-sha"
 
 if [[ -n $INPUT_PATH ]]; then
@@ -205,7 +210,7 @@ else
         PREVIOUS_SHA=$GITHUB_EVENT_PULL_REQUEST_BASE_SHA && exit_status=$? || exit_status=$?
       fi
 
-      if ! git diff --name-only --ignore-submodules=all "$PREVIOUS_SHA"..."$CURRENT_SHA" 1>/dev/null 2>&1; then
+      if ! git diff --name-only --ignore-submodules=all "$PREVIOUS_SHA$DIFF$CURRENT_SHA" 1>/dev/null 2>&1; then
         PREVIOUS_SHA=$(git rev-parse origin/"$TARGET_BRANCH" 2>&1) && exit_status=$? || exit_status=$?
       fi
     fi